Abductive Argument

An argument that attempts to provide the best explanation possible of certain other phenomena as its conclusion. Also known as inference to the best explanation.


A group of propositions, one of which, the conclusion, is (supposed to be) supported by the others, known as the premises.

Cogent Argument

A strong inductive or abductive argument with true premises. If an argument is cogent, then its conclusion is likely to be true.


The proposition in an argument that the premises are supposed to be supporting.

Conclusion Markers

Words that generally indicate that what follows is a conclusion, e.g. “therefore,” “thus,” “consequently.”


A proposition of the form “If A then B,” connecting two simpler propositions A and B. The A in a conditional is known as the antecedent, and B the consequent.


A counterexample is a scenario in which the premises of the argument are true while the conclusion is false. If an argument has a counterexample, it is not valid.

Declarative Sentences

Sentences which communicate that something is, or is not, the case. For example, “Bob won the 50m freestyle.” Declarative sentences can be contrasted with those that pose questions, called interrogative sentences, and those which deliver commands, known as imperative sentences. (Declarative sentences are also known as indicative sentences)

Deductive Argument

An argument that aims to be valid.


Arguments which leave certain premises unstated.


A systematic fault within arguments, leading them to be weak in some sense. Formal fallacies are faults due to the form of the argument, and informal fallacies are faults due to the content of the argument.

Independent Premises

Premises which aim to provide sufficient support on their own for the truth of the conclusion.

Inductive Argument

An argument that moves from observed instances of a certain phenomenon to unobserved instances of the same phenomenon.


A psychological act that links premises to a conclusion in an argument.

Intermediate Premises

Premises which attempt to directly support not the conclusion of an argument, but another premise.

Joint Premises

Premises which only provide support for the truth of the conclusion when combined.

Logical Connectives

Those parts of a language which, according to formal logic, play a significant role within the (in-)validity of an argument.

Logical Form

The deep, hidden, form of an argument due to the occurrence of the logical connectives within it. According to formal logic, logical form plays a significant role in dictating the (in-)validity of an argument.

Logically Implies

One proposition P logically implies another Q if whenever P is true, Q is also true. Arguments in which the premises logically imply the conclusion are known as valid arguments.

Necessary Condition

An event or proposition which is required for another event to occur or proposition to be true. Conditionals express that the consequent is a necessary condition for the antecedent.

Premise Markers

Words that generally indicate what follows is a premise, e.g. “given that,” “as,” “since.”


The propositions within the argument advanced to support the conclusion.


The unambiguated meaning of declarative sentences.

Propositional Logic

(Also known as sentential logic.) A formal logic used by philosophers which studies the logical relationships between propositions by distinguishing between atomic propositions, such as “Bob likes swimming” and “Bob won the 50m freestyle,” and the special logical terms which connect these propositions, known as the logical connectives. Examples of these connectives are “and” (known as conjunction), “or” (known as disjunction), “not” (known as negation), and “if...then…” (known as the material conditional). According to propositional logic, the validity of arguments can often be explained in terms of the behaviour of the logical connectives within the arguments.

Sound Argument

A valid argument with actually true premises. Thus, if an argument is sound, its conclusion must be true.

Strong Argument

An inductive or abductive argument in which the premises make the conclusion likely to be true.

Sufficient Condition

An event or proposition which ensures that another event occurs or another proposition is true. Conditionals express that the antecedent is a sufficient condition for the consequent.

Valid Argument

An argument in which it is impossible for the premises to be true and the conclusion false.

Weak Argument

An inductive or abductive argument in which the premises fail to make the conclusion likely to be true.


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Introduction to Philosophy: Logic Copyright © 2020 by Bahram Assadian; Matthew Knachel; Cassiano Terra Rodrigues; Michael Shaffer; Nathan Smith; Benjamin Martin (Book Editor); and Christina Hendricks (Series Editor) is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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